Polycrystalline diamond constructions &amp; methods of making same

ABSTRACT

A polycrystalline diamond construction has a body of polycrystalline diamond (PCD) material; and a cemented carbide substrate bonded to the body of polycrystalline material along an interface. The cemented carbide substrate includes tungsten carbide particles bonded together by a binder material, the binder material comprising an alloy of Co, Ni and Cr; and the tungsten carbide particles form at least around 70 weight percent and at most around 95 weight percent of the substrate. The cemented carbide substrate has a bulk volume, the bulk volume of the cemented carbide substrate has at least around 0.1 vol. % of inclusions of free carbon having a largest average size in any one or more dimensions of less than around 40 microns.

FIELD

This disclosure relates to polycrystalline diamond (PCD) constructionsand methods of making such constructions, and tools comprising the same,particularly but not exclusively for use in rock degradation ordrilling, or for boring into the earth.

BACKGROUND

Polycrystalline superhard materials, such as polycrystalline diamond(PCD) and polycrystalline cubic boron nitride (PCBN) may be used in awide variety of tools for cutting, machining, drilling or degrading hardor abrasive materials such as rock, metal, ceramics, composites andwood-containing materials. In particular, tool inserts in the form ofcutting elements comprising PCD material are widely used in drill bitsfor boring into the earth to extract oil or gas. The working life ofsuperhard tool inserts may be limited by fracture of the superhardmaterial, including by spalling and chipping, or by wear of the toolinsert.

Cutting elements such as those for use in rock drill bits or othercutting tools typically have a body in the form of a substrate which hasan interface end/surface and a superhard material which forms a cuttinglayer bonded to the interface surface of the substrate by, for example,a sintering process. The substrate is generally formed of a tungstencarbide-cobalt alloy, sometimes referred to as cemented tungsten carbideand the superhard material layer is typically polycrystalline diamond(PCD), polycrystalline cubic boron nitride (PCBN) or a thermally stableproduct TSP material such as thermally stable polycrystalline diamond.

Polycrystalline diamond (PCD) is an example of a superhard material(also called a superabrasive or ultra hard material) comprising a massof substantially inter-grown diamond grains, forming a skeletal massdefining interstices between the diamond grains. PCD material typicallycomprises at least about 80 volume % of diamond and is conventionallymade by subjecting an aggregated mass of diamond grains to an ultra-highpressure of greater than about 5 GPa, and temperature of at least about1,200° C., for example. A material wholly or partly filling theinterstices may be referred to as filler or binder material.

PCD is typically formed in the presence of a sintering aid such ascobalt, which promotes the inter-growth of diamond grains. Suitablesintering aids for PCD are also commonly referred to as asolvent-catalyst material for diamond, owing to their function ofdissolving, to some extent, the diamond and catalysing itsre-precipitation. A solvent-catalyst for diamond is understood be amaterial that is capable of promoting the growth of diamond or thedirect diamond-to-diamond inter-growth between diamond grains at apressure and temperature condition at which diamond is thermodynamicallystable. Consequently the interstices within the sintered PCD product maybe wholly or partially filled with residual solvent-catalyst material.Most typically, PCD is often formed on a cobalt-cemented tungstencarbide substrate, which provides a source of cobalt solvent-catalystfor the PCD. Materials that do not promote substantial coherentintergrowth between the diamond grains may themselves form strong bondswith diamond grains, but are not suitable solvent-catalysts for PCDsintering.

Cemented tungsten carbide which may be used to form a suitable substrateis formed from carbide particles being dispersed in a cobalt matrix bymixing tungsten carbide particles/grains and cobalt together thenheating to solidify. To form the cutting element with a superhardmaterial layer such as PCD or PCBN, diamond particles or grains or CBNgrains are placed adjacent the cemented tungsten carbide body in arefractory metal enclosure such as a niobium enclosure and are subjectedto high pressure and high temperature so that inter-grain bondingbetween the diamond grains or CBN grains occurs, forming apolycrystalline superhard diamond or polycrystalline CBN layer.

In some instances, the substrate may be fully cured prior to attachmentto the superhard material layer whereas in other cases, the substratemay be green, that is, not fully cured. In the latter case, thesubstrate may fully cure during the HTHP sintering process. Thesubstrate may be in powder form and may solidify during the sinteringprocess used to sinter the superhard material layer.

Ever increasing drives for improved productivity in the earth boringfield place ever increasing demands on the materials used for cuttingrock. Specifically, cutting tools with improved resistance to variousfailure mechanisms such are required to achieve faster cut rates andlonger tool life.

Cutting elements or tool inserts comprising PCD material are widely usedin drill bits for boring into the earth in the oil and gas drillingindustry. Rock drilling and other operations require certain mechanicalproperties such as high abrasion resistance, impact resistance, erosionand corrosion resistance and high fracture toughness.

Cutters formed of the most wear resistant grades of PCD material bondedto cemented carbide substrates usually suffer from a catastrophicfracture before the cutter has worn out as, during the use of thesecutters, cracks grow until they reach a critical length at whichcatastrophic failure can occur, namely when a large portion of the PCDand/or cemented carbide substrate breaks away. These long, fast growingcracks encountered during use of conventionally sintered PCD cutters mayresult in short tool life.

Furthermore, despite their high strength, polycrystalline diamond (PCD)materials are usually susceptible to impact fracture due to their lowfracture toughness. Improving fracture toughness without adverselyaffecting the material's high strength and abrasion resistance which arecritical for the material's ability to cut through rock, for example, isa challenging task.

Polycrystalline diamond (PCD) is a super-hard, also known assuperabrasive, material comprising a mass of inter-grown diamond grainsand interstices between the diamond grains. PCD may be made bysubjecting an aggregated mass of diamond grains to an ultra-highpressure and temperature. A material wholly or partly filling theinterstices may be referred to as filler material. PCD may be formed inthe presence of a sintering aid such as cobalt, which is capable ofpromoting the inter-growth of diamond grains and can also act as atough, ductile and impact-resistance binder ensuring a certain level ofPCD fracture toughness. The sintering aid may be referred to as acatalyst/binder material for diamond, owing to its function ofdissolving diamond to some extent and catalysing its re-precipitation. Acatalyst/binder for diamond is understood to be a material that iscapable of promoting the growth of diamond or the directdiamond-to-diamond inter-growth between diamond grains at a pressure andtemperature condition at which diamond is thermodynamically stable aswell as to bound diamond grains together forming a superhard and toughmaterial. Consequently, the interstices within the sintered PCD productmay be wholly or partially filled with residual catalyst/bindermaterial. PCD may be formed on a WC—Co cemented carbide substrate, whichmay provide a source of cobalt catalyst/binder for the PCD.

PCD may be used in a wide variety of tools for cutting, machining,drilling or degrading hard or abrasive materials such as rock, metal,ceramics, composites and wood-containing materials. For example, PCDelements may be used as cutting elements on drill bits used for boringinto the earth in the oil and gas drilling industry. Such cuttingelements for use in oil and gas drilling applications are typicallyformed of a layer of PCD bonded to a cemented carbide substrate.

A known problem with respect to the fabrication of conventional PCDcutting elements is related to the formation of numerous precipitates ofWC, in the form of platelets, at the interface of the body of PCDmaterial with the cemented carbide substrate, which are typicallyreferred to in literature as “WC plumes”. The presence of such plumes atthe interface leads to reduced performance of the PCD cutting elementsin different applications. A common viewpoint on a reason for theformation of WC plumes is the presence of high amounts of tungstendissolved in the binder of conventional cemented carbide substrates. Itis well known that the solubility of tungsten in the liquid Co-basedbinder of cemented carbides is indirectly proportional to the totalcarbon content (I. Konyashin. Cemented Carbides for Mining, Constructionand Wear Parts, Comprehensive Hard Materials, Elsevier Science andTechnology, Editor-in-Chief V. Sarin, 2014, 425-251), so that a lowercarbon content in cemented carbides corresponds to a higher amount oftungsten dissolved in the carbide binder. When liquid Co-based bindersstart infiltrating the PCD layer during sintering they become saturatedwith carbon, due to its diffusion from the PCD layer, and an excessiveamount of tungsten dissolved in the binder precipitates as platelet-likeWC plumes at the PCD/carbide interface.

Another major problem experienced with conventional PCD cutters is therelatively low erosion/corrosion resistance of the carbide substrate ofthe cutter to which the PCD layer is attached. This may result in thecarbide substrate being eroded and/or dissolved very quickly during thedrilling process due to the impact of mud forming on the carbidesubstrate from the coolants used in the drilling process and containingabrasive particles. A worn and eroded carbide substrate cannot supportthe PCD layer attached thereto, with the result that the whole cuttermay fail.

There is therefore a need for a PCD composite construction comprising abody of PCD material bonded to a substrate that has good or improvedmechanical properties such as fracture toughness and impact resistance,and good or improved erosion and/or corrosion resistance, as well as amethod of forming such composites.

SUMMARY

Viewed from a first aspect there is provided a polycrystalline diamondconstruction comprising:

-   -   a body of polycrystalline diamond (PCD) material; and    -   a cemented carbide substrate bonded to the body of        polycrystalline material along an interface; wherein    -   the cemented carbide substrate comprises tungsten carbide        particles bonded together by a binder material, the binder        material comprising an alloy, the alloy comprising any one or        more of Co, Ni and Cr; and    -   the tungsten carbide particles form at least around 70 weight        percent and at most around 95 weight percent of the substrate;    -   wherein the cemented carbide substrate has a bulk volume, the        bulk volume of the cemented carbide substrate comprising at        least around 0.1 vol. % to around 3 vol % of inclusions of any        one or more of free carbon, SP²-hybridised carbon or        SP³-hybridised carbon, the inclusions having a largest average        size in any one or more dimensions of less than around 40        microns.

Viewed from a second aspect there is provided a method of making thepolycrystalline diamond construction of any one of the preceding claims,the method comprising:

-   -   milling a tungsten carbide powder with a binder material and a        mass of carbon to form a milled powder, the binder material        comprising any one or more of Co, Ni, and Cr, and/or a chromium        carbide; and the mass of carbon comprising any one or more of        graphite or amorphous carbon in an amount corresponding to the        equivalent carbon content (ETC) with respect to the milled        powder of equal to or more than around 6.2 wt. %;    -   compacting the milled powder to form a green body;    -   sintering the green body in a vacuum or inert gas atmosphere to        form a first pre-composite body;    -   sintering the first pre-composite body to form a cemented        carbide substrate;    -   placing the cemented carbide substrate into a cannister and        adding a mass of diamond grains or particles to form a second        pre-sinter assembly; and

treating the second pre-sinter assembly in the presence of acatalyst/solvent material for diamond at an ultra-high pressure ofaround 6 GPa or greater and a temperature at which the diamond materialis more thermodynamically stable than graphite to sinter together thediamond grains to form the polycrystalline diamond compact element.

Viewed from a further aspect there is provided a tool comprising thepolycrystalline diamond construction defined above, the tool being forcutting, milling, grinding, drilling, earth boring, rock drilling orother abrasive applications.

The tool may comprise, for example, a drill bit for earth boring or rockdrilling, a rotary fixed-cutter bit for use in the oil and gas drillingindustry, or a rolling cone drill bit, a hole opening tool, anexpandable tool, a reamer or other earth boring tools.

Viewed from another aspect there is provided a drill bit or a cutter ora component therefor comprising the polycrystalline diamond constructiondefined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various versions will now be described by way of example and withreference to the accompanying drawings in which:

FIG. 1 is a schematic perspective view of an example PCD cutter elementfor a drill bit for boring into the earth;

FIG. 2 is a is a schematic partial cross-section through an example of aPCD cutter element;

FIG. 3 a is an image of the microstructure of a substrate for an examplePCD construction before sintering with diamond grains to form theexample PCD construction;

FIG. 3 b is an image of the microstructure of the substrate of FIG. 3 aafter sintering with diamond grains to form the example PCDconstruction;

FIG. 4 a is an image of the microstructure of a substrate for a furtherexample PCD construction before sintering with diamond grains to formthe example PCD construction;

FIG. 4 b is an image of the microstructure of the substrate of FIG. 4 aafter sintering with diamond grains to form the example PCDconstruction;

FIG. 5 is a vertical section of the W—C—Co phase diagram through thecarbon angle with a cobalt content of 20 mass %; and

FIG. 6 is a vertical section of the W—C—Ni phase diagram through thecarbon angle with a cobalt content of 20 mass %.

DESCRIPTION

As used herein, a “superhard material” is a material having a Vickershardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN)material are examples of superhard materials.

As used herein, a “superhard construction” means a constructioncomprising a body of polycrystalline superhard material. In such aconstruction, a substrate may be attached thereto.

As used herein, polycrystalline diamond (PCD) is a type ofpolycrystalline superhard (PCS) material comprising a mass of diamondgrains, a substantial portion of which are directly inter-bonded witheach other and in which the content of diamond is at least about 80volume percent of the material. In one exemplary PCD material,interstices between the diamond grains may be at least partly filledwith a binder material comprising a catalyst for diamond. As usedherein, “interstices” or “interstitial regions” are regions between thediamond grains of PCD material. In exemplary of PCD material,interstices or interstitial regions may be substantially or partiallyfilled with a material other than diamond, or they may be substantiallyempty. PCD material may comprise at least a region from which catalystmaterial has been removed from the interstices, leaving interstitialvoids between the diamond grains.

A “catalyst material” for a superhard material is capable of promotingthe growth or sintering of the superhard material.

The term “substrate” as used herein means any substrate over which thesuperhard material layer is formed. For example, a “substrate” as usedherein may be a transition layer formed over another substrate.

As used herein, the term “integrally formed” regions or parts areproduced contiguous with each other and are not separated by a differentkind of material.

In an example as shown in FIG. 1 , a cutting element 1 includes asubstrate 10 with a layer of superhard material 12 formed on thesubstrate 10. The substrate 10 may be formed of a hard material such ascemented tungsten carbide. The superhard material 12 may be, forexample, polycrystalline diamond (PCD), or a thermally stable productsuch as thermally stable PCD (TSP). The cutting element 1 may be mountedinto a bit body such as a drag bit body (not shown) and may be suitable,for example, for use as a cutter insert for a drill bit for boring intothe earth.

The exposed top surface of the superhard material opposite the substrateforms the cutting face 14, which is the surface which, along with itsedge 16, performs the cutting in use.

At one end of the substrate 10 is an interface surface 18 that forms aninterface with the superhard material layer 12 which is attached theretoat this interface surface. As shown in the example of FIG. 1 , thesubstrate 10 is generally cylindrical and has a peripheral surface 20and a peripheral top edge 22.

As used herein, a PCD grade is a PCD material characterised in terms ofthe volume content and size of diamond grains, the volume content ofinterstitial regions between the diamond grains and composition ofmaterial that may be present within the interstitial regions. A grade ofPCD material may be made by a process including providing an aggregatemass of diamond grains having a size distribution suitable for thegrade, optionally introducing catalyst material or additive materialinto the aggregate mass, and subjecting the aggregated mass in thepresence of a source of catalyst material for diamond to a pressure andtemperature at which diamond is more thermodynamically stable thangraphite and at which the catalyst material is molten. Under theseconditions, molten catalyst material may infiltrate from the source intothe aggregated mass and is likely to promote direct intergrowth betweenthe diamond grains in a process of sintering, to form a PCD structure.The aggregate mass may comprise loose diamond grains or diamond grainsheld together by a binder material and said diamond grains may benatural or synthesised diamond grains.

Different PCD grades may have different microstructures and differentmechanical properties, such as elastic (or Young's) modulus E, modulusof elasticity, transverse rupture strength (TRS), toughness (such asso-called K₁C toughness), hardness, density and coefficient of thermalexpansion (CTE). Different PCD grades may also perform differently inuse. For example, the wear rate and fracture resistance of different PCDgrades may be different.

All of the PCD grades may comprise interstitial regions filled withmaterial comprising cobalt metal, which is an example of catalystmaterial for diamond.

The PCD structure 12 may comprise one or more PCD grades.

FIG. 2 is a cross-section through a PCD material which may form thesuper hard layer 2 of FIG. 1 in an example cutter. During formation of aconventional polycrystalline diamond construction, the diamond grains 22are directly interbonded to adjacent grains and the interstices 24between the grains 22 of super hard material such as diamond grains inthe case of PCD, may be at least partly filled with a non-super hardphase material. This non-super hard phase material, also known as afiller material, may comprise residual catalyst/binder material, forexample cobalt, nickel or iron.

Example PCD constructions are further described with reference to FIGS.3 a to 6. The examples of such PCD constructions include a body ofpolycrystalline diamond material (PCD), bonded to a cemented carbidesubstrate along an interface. The cemented carbide substrate includestungsten carbide particles bonded together by a binder material, thebinder material comprising an alloy of Co, Ni and Cr. The tungstencarbide particles form at least around 70 weight percent and at mostaround 95 weight percent of the substrate. The bulk volume of thecemented carbide substrate comprises at least around 0.1 vol. % toaround 3 vol %, or in some examples around 2.5 vol % or around 2 vol %of inclusions of any one or more of free carbon, SP²-hybridised carbon,or SP³-hybridised carbon having a largest average size in any one ormore dimensions of less than around 40 microns.

In some examples, the inclusions may comprise any one or more of freecarbon, diamond, and/or graphite.

have an average size of less than around 30 microns, and in otherexamples the inclusions have an average size of less than around 10microns.

The bulk volume of the cemented carbide substrate may, in some examples,comprise at least around 0.3 vol. % of inclusions.

The alloy in the binder material of the substrate may, for example,comprise between about 10 to about 80 wt. % Ni, between about 0.5 to 10wt. % Cr, and the remainder wt % comprise Co.

In other examples, the alloy in the binder material of the substrate maycomprise up to around 50 wt. % Fe.

In further examples, the alloy in the binder material of the substratecomprises between about 0.1 to about 4 wt. % tungsten and between about0.05 to about 5 wt. % carbon in solid solution form, and in otherexamples, the alloy in the binder material comprises at least about 0.1weight percent to at most about 5 weight percent of any one or more ofV, Ta, Ti, Mo, Zr, Nb, Hf in the form of a solid solution or a carbidephase.

The alloy in the binder material may comprise at least about 0.1 weightpercent and at most about 2 weight percent of any one or more of Re, Ru,Rh, Pd, Re, Os, Ir and Pt in solid solution.

The cemented carbide substrate may, for example, have a thickness fromthe interface with the body of PCD material of at least around 0.1 mm,or at least around 0.2 mm, or at least around 0.3 mm.

In additional examples, a second cemented carbide substrate may bebonded to the cemented carbide substrate along a second interface whichis opposite the interface with the body of PCD material, the secondsubstrate comprising substantially no inclusions of free carbon,SP²-hybridised carbon or SP³-hybridised carbon, such as diamond orgraphite.

In some examples, an interfacial region between the cemented carbidesubstrate and the body of PCD material comprises substantially noplatelet-like WC grains.

The example polycrystalline diamond constructions may be made by millinga tungsten carbide powder with a binder material and a mass of carbon toform a milled powder, the binder material comprising Co, Ni, and Cr, ora chromium carbide, and the mass of carbon comprising any one or more ofgraphite or amorphous carbon in an amount corresponding to theequivalent carbon content (ETC) with respect to the milled powder, forexample the WC in the milled powder, of equal to or more than around 6.2wt. %. The milled powder is compacted to form a green body which is thensintered in a vacuum or inert gas atmosphere to form a firstpre-composite body. The first pre-composite body is then sintered toform a cemented carbide substrate. The cemented carbide substrate isplaced into a cannister and a mass of diamond grains or particles isadded to form a second pre-sinter assembly. The second pre-sinterassembly is subsequently treated in the presence of a catalyst/solventmaterial for diamond at an ultra-high pressure of around 6 GPa orgreater, such as for example, around 6.8 GPa, or around 7 GPa, or around7.7 Pa, or 8 GPa or greater and at a temperature at which the diamondmaterial is more thermodynamically stable than graphite, to sintertogether the diamond grains to form the polycrystalline diamond compactelement. The bulk volume of the substrate of the so formed PCDconstructions has at least around 0.1 vol. % to around 3 vol % ofinclusions of any one or more of free carbon, SP²-hybridised carbon orSP³-hybridised carbon, such as graphite or diamond, having a largestaverage size in any one or more dimensions of less than around 40microns

The step of sintering the green body to form the pre-composite body mayinclude heating the green body up to a temperature of at least around300° C. in a vacuum followed by annealing for at least around 5 minutes.

In some examples, prior to the step of placing the cemented carbidesubstrate into the canister, a cemented carbide disc of at least around2 mm in thickness may be formed which comprises binder material havingbetween around 10 to around 80 wt. % Ni, between about 0.5 to about 10wt. % Cr and the remainder weight percent comprising Co, and at leastabout 0.1 vol. % carbon inclusions in form of graphite. An additionalcemented carbide post having a binder material comprising about 10 toabout 90 wt. % Ni, about 0.2 to about 15 wt. % Cr and the remainderweight percent Co may also be formed and the disc and the post may thenbe bonded together by sintering either at ambient conditions or atultra-high pressure to form an example cemented carbide substrate forplacing into the canister with the mass of diamond grains or particles.

In such examples, the milled powder may be pressed onto or around acemented carbide post having a binder material comprising about 10 toabout 90 wt. % Ni, about 0.2 to about 15 wt. % Cr and the remainderweight percent Co to form the green body; and the step of sintering thegreen body may, for example, comprise sintering the posts with a layerof the milled powder at a temperature in the range of between about1350° C. to about 1400° C. for between about 10 to about 60 minutes in avacuum or protective gas.

In an alternative example, the step of bonding the disc and the post maycomprise brazing by, for example, placing a barrier interlayer betweenthe post and the disc, the barrier layer having a thickness of at leastaround 10 μm and comprising any one or more of a metal, a metal carbide,nitride or carbonitride.

In any one or more of the example methods, after the step of sinteringthe first pre-composite body to form the cemented carbide substrate themethod may further comprise the step of selectively de-carburizing aportion of the cemented carbide substrate in a hydrogen atmosphere or anatmosphere of CO₂ at a temperature of at least around 700° C. for atleast around 1 hour, the portion having a thickness of at least around50% of the total height of the cemented carbide substrate.

In any one or more of the example methods, after the step of sinteringthe first pre-composite body to form the cemented carbide substrate, themethod may further comprise carburizing the cemented carbide substratein an atmosphere comprising any one or more of a hydrocarbon gas, aninert gas or hydrogen at a temperature of at least around 1350° C. forbetween around 1 hour to around 10 hours.

The step of carburizing may comprise treating the cemented carbidesubstrate or green body with a powder mixture comprising any one or moreof carbon black, graphite or a carbon-containing precursor in anatmosphere comprising any one or more of an inert gas, hydrogen or agaseous mixture comprising hydrocarbons at a temperature of above around1000° C. for at least around 1 hour.

In some examples, the step of treating the second pre-sinter assemblycomprises subjecting the assembly to a sufficiently high temperature forthe catalyst/solvent to be in a liquid state and to a first pressure atwhich diamond is thermodynamically stable, reducing the first pressureto a second pressure at which the diamond is thermodynamically stable,the temperature being maintained sufficiently high to maintain thecatalyst/binder in the liquid state, reducing the temperature tosolidify the catalyst/binder and then reducing the pressure and thetemperature to an ambient condition to form the example body ofpolycrystalline diamond material bonded to the cemented carbidesubstrate.

The PCD constructions according to any one of the examples may beincluded in or used as a tool for cutting, milling, grinding, drilling,earth boring, rock drilling or other abrasive applications, such as adrill bit for earth boring or rock drilling. The tool comprising theexample PCD construction may comprise a rotary fixed-cutter bit for usein the oil and gas drilling industry, such as a rolling cone drill bit,a hole opening tool, an expandable tool, a reamer or another earthboring tool. A drill bit or a cutter or a component therefor maycomprise any one or more of the example PCD constructions.

The formation of examples of PCD constructions as shown in FIGS. 3 a to4 b is discussed in more detail below with reference to the followingexamples, which are not intended to be limiting, and with reference toFIGS. 5 and 6 .

A control batch of conventional cemented carbide substrates for a PCDconstruction was produced by forming a 5 kg powder mixture by milling,in a ball mill, a WC powder having a mean grain size of about 1.3 μm,8.1 wt. % Co powder having a mean grain size of nearly 1 μm, 4.0 wt. %Ni powder with a mean grain size of roughly 2.5 μm, and 0.4 wt. % Cr3C2powder with mean grain size 1.6 μm together with 30 kg carbide balls and100 g paraffin wax. Once the powder had dried, it was granulated andcompacted to form substrates for PCD constructions in the form of greenbodies. The equivalent total carbon (ETC) in the cemented carbidematerial was determined to be 6.12 percent with respect to WC.

The green bodies were sintered by means of a Sinterhip™ furnace at 1,420degrees centigrade for about 75 min, 45 min of which was carried out invacuum and 30 min of which was carried out in a HIP apparatus in an Arat a pressure of about 40 bars.

Afterwards a layer of polycrystalline diamond was bonded to each of thecontrol carbide substrates by placing the individual substrates into arespective into a cannister and adding a mass of diamond grains orparticles to form a second pre-sinter assembly. The second pre-sinterassembly was subsequently treated in the presence of a catalyst/solventmaterial for diamond at an ultra-high pressure of around 6 GPa orgreater, in some examples, around 7 Gpa or greater, and at a temperatureof around 1400 degrees C. to sinter together the diamond grains to formthe polycrystalline diamond construction.

EXAMPLE 1

An experimental batch of carbide substrates for a first example PCDconstruction was produced using the same procedure described above forthe control batch except 0.2 wt. % carbon was added to the powdermixture that was to be milled. The equivalent total carbon (ETC) in thecemented carbide material was determined in this first example to be6.32 percent with respect to WC.

Afterwards a layer of polycrystalline diamond was bonded to the carbidesubstrates by use of high-pressure and high-temperatures (HPHT)procedures described above to produce a first example set of PCDconstructions.

EXAMPLE 2

Another experimental batch of carbide substrates for forming a secondexample PCD construction was produced using the same procedure describedabove for the control batch except 0.5 wt. % carbon was added to thepowder mixture that was to be milled. The equivalent total carbon (ETC)in the cemented carbide material was determined to be 6.62 percent withrespect to WC.

Afterwards a layer of polycrystalline diamond was bonded to the carbidesubstrates by use of high-pressure and high-temperatures (HPHT)procedures described above to produce a second example set of PCDconstructions.

The magnetic coercivity and other properties of the control carbidesubstrates and the example carbide substrates was determined usingconventional procedures. In particular, the magnetic coercivity of thecontrol carbide substrates was found to be equal to roughly 170 Oe,their magnetic moment to be equal to 13.2 Gcm³/g and density to be equalto 14.15 g/cm³.

By contrast, for the constructions formed according to Example 1, themagnetic coercivity of the carbide substrates was found to be equal toroughly 169 Oe, their magnetic moment to be equal to 13.6 Gcm³/g anddensity to be equal to 14.0 g/cm³.

For the constructions formed according to Example 2, the magneticcoercivity of the carbide substrates was found to be equal to roughly170 Oe, their magnetic moment to be equal to 13.7 Gcm³/g and density tobe equal to 14.0 g/cm³.

To examine mechanical properties and erosion-corrosion resistance of thecontrol carbide substrates, the PCD layer was removed by EDM cutting.The Vickers hardness of the substrates was determined using conventionaltesting procedures to be equal to HV₂₀=1230, the transverse rupturestrength was determined to be equal to 3700 MPa and the indentationfracture toughness was determined to be equal to 15.3 MPa m^(1/2).

The control cemented carbide substrates were also examined in an erosiontest in a recirculating rig generating an impinging jet of liquid-solidslurry under the following testing conditions: temperature—50° C.,impingement angle—45°, slurry velocity—20 m/s, pH—8.02, duration—3 hrs,slurry composition in 1 cubic meter water: Bentonite—40 kg; Na2CO3—2 kg,carboxymethyl cellulose—3 kg, polyacrylamide solution—5 l, quartz sand—1kg. The weight which provides an indication of corrosion/erosionresistance loss was found to be equal to 3.82 mg.

To examine mechanical properties of the carbide substrates formedaccording to Example 1, these were tested under the same conditions asthe control substrates after removing the PCD layer by EDM cutting. TheVickers hardness of the substrates of Example 1 was determined to beequal to HV₂₀=1240, the transverse rupture strength was determined to beequal to 2860 MPa and the indentation fracture toughness was determinedto be equal to 15.5 MPa m^(1/2).

To examine mechanical properties of the carbide substrates formedaccording to Example 2, these were tested under the same conditions asthe control substrates after removing the PCD layer by EDM cutting. TheVickers hardness of the substrates formed according to Example 2 wasdetermined to be equal to HV₂₀=1250, the transverse rupture strength wasdetermined to be equal to 3040 MPa and the indentation fracturetoughness was determined to be equal to about 19 MPa m^(1/2).

In addition to the mechanical properties, the microstructures of thecontrol substrates and those produced according to Examples 1 and 2above were examined using conventional high resolution TEM procedures,and were examined after initial sintering of the substrates and againafter the sintering stage used to form the PCD construction in which thediamond grains are sintered and bonded to the substrates.

The microstructure of the control carbide substrates when examined usingconventional high resolution TEM, and/or SEM procedures was found to befree of free carbon and η-phase, both before and after second sintering.

Images of the microstructure for the constructions formed according toExample 1 are shown in FIGS. 3 a and 3 b , before and after secondsintering respectively. As can be seen from FIG. 3 a , before the secondsintering stage, the microstructure was found to comprise inclusions offree carbon and, as seen in FIG. 3 b , after second sintering to formthe PCD construction of Example 1, the microstructure comprisessignificantly less inclusions of free carbon in comparison with thatbefore performing the second HPHT procedure, and they are finely anduniformly distributed in the microstructure. Again using the standardSEM procedure, the volume percentage of the inclusions of free carbonshown in FIG. 3 b in the substrate of the example PCD construction wasdetermined to be around 0.4 vol. % and these inclusions of free carbonhad a largest average size in any one or more dimensions of less thanaround 40 microns.

Images of the microstructure for the constructions formed according toExample 2 are shown in FIGS. 4 a and 4 b , before and after secondsintering respectively. As can be seen from FIG. 4 a , before the secondsintering stage, the microstructure of the substrate was found tocomprise inclusions of free carbon and, as seen in FIG. 4 b , aftersecond sintering to form the PCD construction of Example 2, themicrostructure of the example substrate comprises significantly lessinclusions of free carbon in comparison with that before performing thesecond HPHT procedure, and they are finely and uniformly distributed inthe microstructure. Again using the standard SEM procedure, the volumepercentage of the inclusions of free carbon in the example substrateshown in FIG. 4 b in the example PCD construction was determined to bearound 1.3 vol. % and the inclusions of free carbon in this examplesubstrate had a largest average size in any one or more dimensions ofless than around 40 microns.

The erosion-corrosion resistance of the carbide substrates formedaccording to Examples 1 and 2 was tested in the same manner as describedabove for the control substrates and was found to be equal to around5.65 mg.

The image analysis also showed that for the example PCD constructions noWC platelets (“plumes”) were found at the interface of the body of PCDmaterial and the substrate.

It may therefore be seen that the PCD constructions formed according toExamples 1 and 2 show a favourable combination of mechanical properties,including significantly improved fracture toughness over the control PCDconstructions, and good erosion-corrosion resistance. Whilst not wishingto be bound by any particular theory, it is believed this may beattributed to or assisted by the surprising and unusual microstructureat least of the substrates in the example PCD constructions which areseen to comprise fine carbon inclusions of less than 40 microns in anylargest dimension and which are distributed through the bulk of thesubstrate and, in some examples in substantially homogeneous or uniformdistribution.

The conventional teaching on the influence of free carbon precipitateson cemented carbide mechanical properties is that the presence of suchprecipitates in a cemented carbide microstructure dramatically reduceshardness, toughness and transverse rupture strength (TRS) of the carbidestructure (see for example Suzuki, H., Kubota, H., entitled Theinfluence of binder phase composition on the properties of tungstencarbide-cobalt cemented carbides Planseeberichte fuer Pulvermetallurgie14(2), (1966) 96-109). However, it has been surprisingly found by thepresent applicants that the example constructions formed by the examplemethods which combine a body of PCD material with a cemented carbidesubstrate having a bulk volume comprising at least around 0.1 vol. % upto any one or more of around 3 vol %, or 2.5 vol %, or 2 vol % ofinclusions of free carbon, and/or SP²-hybridised carbon, and/orSP³-hybridised carbon having a largest average size in any one or moredimensions of less than around 40 microns work synergistically andsurprisingly to significantly improve fracture toughness over thecontrol PCD constructions, and, when combined with the cemented carbidesubstrate comprising tungsten carbide particles bonded together by abinder material comprising an alloy of Co, Ni and Cr, and the tungstencarbide particles forming at least around 70 weight percent and at mostaround 95 weight percent of the substrate, synergistically andsurprisingly provide advantageous erosion-corrosion resistance. Whilstnot wishing to be bound by any particular theory, a possible explanationmay be that the applicants have found that carbon solubility in theliquid binders at ultra-high pressures significantly increases and whena large amount of free carbon/SP²-hybridised carbon/SP³-hybridisedcarbon is present in the microstructure in form of large graphiteinclusions as seen in FIGS. 3 a and 4 a before the second sinteringstage, these may be dissolved in the liquid binder during the secondsintering stage, that is during the PCD sintering stage. As a result ofsolidification after the PCD sintering stage, the excess of carbonprecipitates in the substrate in the form of extremely fine anduniformly distributed particles, as shown in FIGS. 3 b and 4 b , whichvery surprisingly do not appear to adversely impact the mechanicalproperties of the PCD construction.

Additionally, it was found that the formation of the WC plumes may besuppressed by in and by the example methods of forming example PCDconstructions.

Also, it is believed that the example methods and in particular additionof the mass of carbon prior to sintering may have desirable sinteringaid properties. Whilst not wishing to be bound by theory, a possibleexplanation may be that, the if the liquid binder is saturated oroversaturated with carbon during PCD press sintering, its melting pointis reduced according to the W—Co—C and W—Ni—C phase diagrams as shown inFIGS. 5 and 6 (see B. Uhrenius, H. Pastor, E. Pauty, on The compositionof Fe—Ni—Co—WC-based cemented carbides, Int. J Refractory Met HardMater., 15(1997)139-149). As a result, a rate of the solid-statedensification of diamond grits obtained before binder melting whenincreasing the temperature of PCD press sintering is reduced compared toconventional sintering techniques of conventional PCD constructions andinfiltration of the PCD table by the liquid binder may occur earlier inthe sintering cycle than in conventional sintering techniques leading toimproved sintering.

While various examples have been described with reference to a number ofexamples, those skilled in the art will understand that various changesmay be made and equivalents may be substituted for elements thereof andthat these examples are not intended to limit the particular examplesdisclosed. In particluar whilst standard SEM and TEM imaging techniquesmay be used to determine the vol % of inclusions, conventional opticalmicroscopy techniques may also be used.

1. A polycrystalline diamond construction comprising: a body ofpolycrystalline diamond (PCD) material; and a cemented carbide substratebonded to the body of polycrystalline material along an interface;wherein the cemented carbide substrate comprises tungsten carbideparticles bonded together by a binder material, the binder materialcomprising an alloy, the alloy comprising any one or more of Co, Ni andCr; and the tungsten carbide particles form at least around 70 weightpercent and at most around 95 weight percent of the substrate; whereinthe cemented carbide substrate has a bulk volume, the bulk volume of thecemented carbide substrate comprising at least around 0.1 vol. % toaround 3 vol % of inclusions of any one or more of free carbon,SP²-hybridised carbon or SP³-hybridised carbon, the inclusions having alargest average size in any one or more dimensions of less than around40 microns.
 2. The polycrystalline diamond construction according toclaim 1, the inclusions in the bulk volume of the cemented carbidesubstrate having an average size of less than around 30 microns.
 3. Thepolycrystalline diamond construction according to claim 1, theinclusions in the bulk volume of the cemented carbide substrate havingan average size of less than around 10 microns.
 4. The polycrystallinediamond construction according to claim 1, wherein the inclusions format least around 0.3 vol % to around 3 vol % of the bulk volume of thecemented carbide substrate.
 5. The polycrystalline diamond constructionaccording to claim 1, wherein the inclusions form at least around 0.1vol % to around 2.5 vol % of the bulk volume of the cemented carbidesubstrate.
 6. (canceled)
 7. The polycrystalline diamond constructionaccording to claim 1, wherein the inclusions any one or more of diamondor graphite.
 8. The polycrystalline diamond construction according toclaim 1, wherein the alloy comprises between about 10 to about 80 wt. %Ni, between about 0.5 to 10 wt. % Cr, and the remainder wt % comprisingCo.
 9. The polycrystalline diamond construction according to claim 1,wherein the alloy in the binder material of the substrate furthercomprises up to around 50 wt. % Fe.
 10. The polycrystalline diamondconstruction according to claim 1, wherein the alloy in the bindermaterial further comprises between about 0.1 to about 4 wt. % tungstenand between about 0.05 to about 5 wt. % carbon in solid solution form.11. The polycrystalline diamond construction according to claim 1,wherein the alloy in the binder material further comprises at leastabout 0.1 weight percent to at most about 5 weight percent of any one ormore of V, Ta, Ti, Mo, Zr, Nb, Hf in the form of a solid solution or acarbide phase.
 12. The polycrystalline diamond construction according toclaim 1, wherein the alloy in the binder material further comprises atleast about 0.1 weight percent and at most about 2 weight percent of anyone or more of Re, Ru, Rh, Pd, Re, Os, Ir and Pt in solid solution. 13.(canceled)
 14. The polycrystalline diamond construction according toclaim 1, further comprising a second cemented carbide substrate bondedto the cemented carbide substrate along a second interface opposite saidinterface with the body of PCD material, the second substrate comprisingsubstantially no inclusions of any one or more of free carbon,SP²-hybridised carbon or SP³-hybridised carbon.
 15. The polycrystallinediamond construction according to claim 1, wherein an interfacial regionbetween the cemented carbide substrate and the body of PCD materialcomprises substantially no platelet-like WC grains.
 16. A method ofmaking the polycrystalline diamond construction of claim 1, the methodcomprising: milling a tungsten carbide powder with a binder material anda mass of carbon to form a milled powder, the binder material comprisingany one or more of Co, Ni, and Cr, and/or a chromium carbide; and themass of carbon comprising any one or more of graphite or amorphouscarbon in an amount corresponding to the equivalent carbon content (ETC)with respect to the milled powder of equal to or more than around 6.2wt. %; compacting the milled powder to form a green body; sintering thegreen body in a vacuum or inert gas atmosphere to form a firstpre-composite body; sintering the first pre-composite body to form acemented carbide substrate; placing the cemented carbide substrate intoa cannister and adding a mass of diamond grains or particles to form asecond pre-sinter assembly; and treating the second pre-sinter assemblyin the presence of a catalyst/solvent material for diamond at anultra-high pressure of around 6 GPa or greater and a temperature atwhich the diamond material is more thermodynamically stable thangraphite to sinter together the diamond grains to form thepolycrystalline diamond compact element.
 17. The method of claim 16,wherein the step of sintering the green body to form the pre-compositebody comprises heating the green body up to a temperature of at leastaround 300° C. in a vacuum followed by annealing for at least around 5minutes.
 18. The method of claim 16, further comprising prior to thestep of placing the cemented carbide substrate into the canister,forming the cemented carbide substrate by: forming a cemented carbidedisc of at least around 2 mm in thickness, the disc comprising bindermaterial comprising between around 10 to around 80 wt. % Ni, betweenabout 0.5 to about 10 wt. % Cr and the remainder weight percentcomprising Co, and between at least about 0.1 vol. % and 3 vol % carboninclusions in the form of graphite; forming a cemented carbide posthaving a binder material comprising about 10 to about 90 wt. % Ni, about0.2 to about 15 wt. % Cr and the remainder weight percent Co; andbonding the disc and the post together by sintering either at ambientconditions or at ultra-high pressure to form the cemented carbidesubstrate for placing into the canister with the mass of diamond grainsor particles.
 19. The method of claim 16, further comprising pressingthe milled powder onto or around a cemented carbide post having a bindermaterial comprising about 10 to about 90 wt. % Ni, about 0.2 to about 15wt. % Cr and the remainder weight percent Co to form the green body; andwherein the step of sintering the green body comprises sintering theposts with a layer of the milled powder at a temperature in the range ofbetween about 1350° C. to about 1400° C. for between about 10 to about60 minutes in a vacuum or protective gas.
 20. The method of claim 18wherein the step of bonding the disc and the post comprises brazing thedisc to the post to bond the disc and the post together.
 21. The methodof claim 20 wherein the step of brazing comprises placing a barrierinterlayer between the post and the disc, the barrier layer having athickness of at least around 10 μm and comprising any one or more of ametal, a metal carbide, nitride or carbonitride.
 22. The method of claim16 further comprising after the step of sintering the firstpre-composite body to form the cemented carbide substrate selectivelyde-carburizing a portion of the cemented carbide substrate in a hydrogenatmosphere or an atmosphere of CO₂ at a temperature of at least around700° C. for at least around 1 hour, the portion having a thickness of atleast around 50% of the total height of the cemented carbide substrate.23. The method of claim 16 further comprising after the step ofsintering the first pre-composite body to form the cemented carbidesubstrate carburizing the cemented carbide substrate in an atmospherecomprising any one or more of a hydrocarbon gas, an inert gas orhydrogen at a temperature of at least around 1350° C. for between around1 hour to around 10 hours.
 24. The method of claim 16 further comprisingcarburizing the green body in an atmosphere comprising any one or moreof a hydrocarbon gas, hydrogen or an inert gas at a temperature of atleast around 1350° C. for between around 1 hour to around 10 hours. 25.The method of claim 23, wherein the step of carburizing comprisestreating the cemented carbide substrate or green body with a powdermixture comprising any one or more of carbon black, graphite or acarbon-containing precursor in an atmosphere comprising any one or moreof an inert gas, hydrogen or a gaseous mixture comprising hydrocarbonsat a temperature of above around 1000° C. for at least around 1 hour.26. The method of claim 23, wherein the step of treating the secondpre-sinter assembly comprises: subjecting the assembly to a sufficientlyhigh temperature for the catalyst/solvent to be in a liquid state and toa first pressure at which diamond is thermodynamically stable; reducingthe first pressure to a second pressure at which the diamond isthermodynamically stable, the temperature being maintained sufficientlyhigh to maintain the catalyst/binder in the liquid state; reducing thetemperature to solidify the catalyst/binder; and reducing the pressureand the temperature to an ambient condition to form a body ofpolycrystalline diamond material bonded to the cemented carbidesubstrate. 27-31. (canceled)